The present invention relates to an improvement to an earth interface. A moisture collecting mesh screen collects moisture from the morning air which is laden with moisture. A conduit feeds this collected moisture to a grounding electrode. At least two collars may be fitted around the known chemically charged hollow grounding electrode installed in a hole. The moisture reduces the surge impedance of the grounding electrode with respect to earth.
xe2x80x9cGroundingxe2x80x9d is the art of making an electrical connection to the earth. That ground connection is actually the interface with earth and through that interface, the grounded system is in electrical contact with the whole earth. Through that interface pass electrical xe2x80x9ceventsxe2x80x9d to and from the related system(s). These electrical xe2x80x9ceventsxe2x80x9d include power from the utility, communications, phone, radio, and other forms of data.
The character of this interface will determine the effectiveness of its function, i.e., how xe2x80x9cgoodxe2x80x9d is the interface and/or is there a reliable, year-round connection to earth. The effectiveness of an interface is usually assessed in terms of its true DC resistance to Mother Earth. However, there is another factor of greater concern to many, that is, the transient response or surge impedance, or the effective inductance of that interface. This factor will determine the effectiveness of that interface for such functions as lightning grounds, RF grounds, electric utility protection equipment grounds and personnel safety under xe2x80x9cground faultingxe2x80x9d conditions.
The earth interface system is an important subsystem. The blind application of standards with little reference to the site character or the impact of seasonal changes will seldom yield an effective ground interface.
When the earth interface system has not been properly engineered, significant system equipment damage persists, personnel safety has been impaired and system performance has been less than ideal.
Finally, the trend toward microelectronics has made electrical and electronic systems even more sensitive to any form of anomalous electrical transients. Grounding, the earth interface, must now be considered a vital function and must be engineered for each site and/or system individually.
Grounding systems perform at least one of the following functions:
1. A Ground, or Earth Reference Electrode. Every electrical or electronic system must be referenced to the earth. This is referred to as xe2x80x9cgroundingxe2x80x9d. The grounding point in that system provides a common reference point for circuits within the system. In many cases, the resistance to earth of that reference point is of little significance. For these systems a Common Point Ground (CPG) will satisfy the functional requirements. These systems are usually totally self-contained or autonomously operated systems requiring no external interfaces except possibly the power, and present no potential for a compromise of personal safety. This form of grounding system, the CPG, mandates a separate connection from each element in the system to that CPG preferably via a separate path. A simple example of this CPG is a single computer terminal where the green wire in the power plug is the reference point.
2. The Lightning Neutralization Ground. Lightning protection grounding system requirements have conventionally been thought to be similar to the preceding, when in truth, they are quite different. A more descriptive title would be: xe2x80x9cLightning Charge Neutralization Systemxe2x80x9d. This comes about because of the nature of atmospheric electricity and the lightning strike mechanism. Storm clouds induce an image charge of equal but opposite potential in the earth beneath the cloud. When a lightning channel terminates on an earthen object, that channel forms a conductive path between the two bodies to permit equalization of the charge between them. Since the charge is induced on the surface of the earth, it follows that all of that charge must move from where it was induced to the strike channel terminus in order to neutralize the charge between earth and that cloud. All this must happen in 20 microseconds or so. If the facility of concern is part of the charged body or is the terminus of the strike, its grounding system must provide the low resistance, low surge impedance path from any point in the system to any other point in the system where the strike may terminate. Therefore, the grounding requirement for lightning protection is not just a low (DC) resistance to ground per se, but an interconnecting ground network that electrically interconnects every vulnerable component of the plant or system of concern with a low surge impedance path.
3. A Universal System. The universal grounding system may require a near perfect interface with the earth. That is, the lower the effective resistance between that system ground point and true earth, the better, safer, or more effective the system will be. This requirement is usually associated with systems that have many interfaces with other systems, or the xe2x80x9coutside worldxe2x80x9d. Typical examples include the electrical utility industry, the telephone central office and large industrial plants. These same systems often require a common point grounding (CPG), a lightning neutralization capability, and a low impedance interface with earth; thus providing a universal grounding (or earth) interface.
Soil augmentation is the process of replacing a portion of the local soil with a more conductive soil, or the replacement of poor (high resistance) soil in the critical areas. The new soil must be introduced around the grounding electrode since that is where it will be most beneficial. For years, a form of clay known as Bentonite has been used for this purpose. Its resistivity is found to be about 2.5 ohm-meters which is reasonably conductive. The usefulness of Bentonite is limited by two unfavorable characteristics:
a. Its volume sensitivity to moisture causes it to shrink away from the rod during long dry seasons, its volume can vary by 300%, thus, dramatically increasing the electrode resistance to earth.
b. Its low porosity limits its ability to conduct moisture and dissolved mineral salts into or through it.
To overcome these negative qualities, the present invention may optionally incorporate a product known as xe2x80x9cGrounding Augmentation Fillxe2x80x9d (GAF(trademark)). GAF(trademark) has a resistivity of about 0.5 ohm-meters, it is highly conductive of both moisture and minerals and is far less susceptible to shrinkage.
The use of a good backfill such as GAF(trademark) can significantly reduce the initial resistivity and the ultimate impedance to earth of a grounding electrode when properly utilized. The best use is for replacing the soil in the immediate area (six to twelve inches) surrounding the grounding electrode.
The present invention adds a moisture collector to a grounding electrode, thereby reducing the resistance between the grounding electrode and the surrounding soil.
Thus, the present invention improves an optimal universal grounding system by adding a moisture collecting system to a state of the art grounding electrode, and further adding an ideal backfill. Thus, even dry soils can be adapted to provide an adequate ground.
The foregoing grounding objectives are achieved by providing a conventional tubular member of an electrically conductive material. The tubular member is filled with a selected metallic salt matched to the soil condition. The tubular member is then buried and surrounded with an osmotically conductive material such as the Grounding Augmentation Fill (GAF(trademark)). The lower portion of the tubular member is a reservoir containing a saturated solution of that salt. The lower portion has provisions for the overflow of the salt from that reservoir so as to maintain a wet interface between the electrode and the GAF(trademark) or a GAF(trademark)/soil mixture.
Two or more conductive rings or collars maybe added to the conventional structure of the hollow tubular member. The rings are nominally twelve to thirty-six inches in diameter, flat, and composed of copper or other highly conductive metal. Special situations could require much larger diameters. The surprising effect of the collars is to increase the effective diameter of the grounding electrode, thereby reducing the surge impedance of the grounding electrode by up to 40% with respect to earth as illustrated by FIG. 33. The collar diameter and position can also be varied to xe2x80x9ctune toxe2x80x9d the grounding electrode to a desired frequency. Use of two or more disks will integrate the backfill and/or soil into the rod and soil interface, thereby increasing the effective diameter of the rod. The surge impedance is thereby reduced. Finally, when a ground augmentation fill is used between the collars it makes better contact with the ground, thereby increasing the effective diameter of the rod to the diameter of the collars.
A preferred embodiment of the invention comprises a grounding electrode installed to provide an electrical interface with a soil for grounding various electrical and lightning protection systems, comprising: an electrode assembly comprising a conductive tubular member having an upper and a lower end and a plurality of holes formed in its lateral wall; at least one conductive collar affixed to the upper end of the conductive tubular member and positioned below the soil""s surface; at least one additional conductive collar affixed to the tubular member below the first conductive collar; a removable filler plug mounted on the upper end of the conductive tubular member; an electrical connector mounted near the upper end of the conductive tubular member for the attachment of electrical connections; an end cap mounted on the lower end of the conductive tubular member; and an osmotic conductor filling a cylindrical hole in the soil and enveloping the portion of the conductive tubular member below the soil surface and contacting the plurality of holes.
The osmotic conductor can comprise some combination of a metallic salt, attapulgite and lignite. The conductive tubular member preferably contains at least one chemical capable of enhancing the soil""s conductivity, the chemical being deposited into the interior of the tubular member so as to fully occupy its interior space. When the conductive tubular member is buried in the soil with the removable filler plug above the turf line, the conductive tubular member, the chemical contained therein and the osmotic conductor together provide a highly conductive interface with the soil. The grounding electrode can be electrically connected to at least one similar grounding electrode to provide a better grounding connection. The diameter(s) of the conductive collar(s) should be at least sufficient to reduce the surge impedance of the grounding electrode assembly.
A moisture collecting screen assembly is mounted near the grounding electrode(s). The moisture laden morning air condenses on the moisture collecting screen. The collected moisture seeps into the adjacent soil, thereby lowering the earth to electrode resistance.
Thus, this invention overcomes the known limitations of the prior art by providing an improved, passively rechargeable via the environment, chemically-activated, highly conductive grounding electrode in combination with a low-resistance soil within its immediate area.
The primary aspect of the present invention is to passively replenish the moisture in a grounding electrode and the surrounding soil with a moisture collector.
Another aspect of the present invention is to provide conductive collars on a hollow, tubular grounding electrode in order to increase the effective diameter of the grounding electrode.
Another aspect of the present invention is to bury the improved grounding electrode in an osmotic conductor, thereby further reducing the surge impedance of the combination.
Other aspects of this invention will appear from the following description and appended claims, reference being made to the accompanying drawings forming a part of this specification wherein like reference characters designate corresponding parts in the several views.
The new, useful and non-obvious improvement claimed herein is a combination of conductive collars affixed to a hollow grounding electrode, wherein this known apparatus is fed with a stream of moisture passively collected from the ambient air. The collars are usually flat, about twelve to thirty-six inches in diameter and preferably composed of copper. The hollow tubular grounding electrode is preferably filled with a metallic salt matched to the soil condition. The lower portion of the electrode has provisions for the overflow of salt from the internal reservoir so as to maintain a preferably wet interface between the electrode and the soil mixture. Finally, the entire assembly is buried in a hole which is filled with a backfill which is a low resistance soil. The collar helps to make the effective diameter of the electrode bigger.
Based on the foregoing, these further aspects are attained:
(a). a reservoir at the end of the electrode generates, maintains, and forces a saturated solution to wet a significant portion of the lower end of the electrode as ground water is admitted into the electrode, said reservoir being fed by a moisture collector.
(b). providing a rechargeable operating concept that permits periodic recharging and a constant feed of the required chemicals into the reservoir;
(c). providing an external osmotic conductor, GAF(trademark), to assure the maintenance of a conductive interface at the most significant location, whereby the osmotic conduction is based on capillary action.
(d). providing ease of inspection and preventative maintenance;
(e). combining the useful features of prior art into this invention, thereby providing an electrode that will satisfy the requirements of even the most stringent applications.